The invention relates to an illuminator apparatus in accordance with the preamble of claim 1. The present invention particularly relates to cooling down an illuminator comprising LEDs.
In connection with prior art LED illuminators, the question of voltage adaptation has to be taken into account while manufacturing such illuminators. LED is an abbreviation of a light emitting diode. When forward current is supplied through a LED, the power remaining in the diode emits light. The drop in voltage of one LED unit is approximately 2.0 to 4.0 V. The drop in voltage is determined according to the current, substantially in accordance with a dynamic release curve of a conventional diode. The drop in voltage, in turn, causes the temperature in the illuminator and all its components to rise.
As technology advances, more and more efficient LEDs whose efficiencies range from 0.1 to up to 5 W have become available on the market. The efficiencies tend to further increase as the technology advances. However, the illuminating efficiency of a LED is of the same order of magnitude as that of a filament lamp, i.e. 6 to 8%. As is typical of all chemical reactions, it is also typical of LEDs that their life expectancy decreases as temperature rises (the Arrhenius equation), i.e. as the drop in voltage increases.
In prior art illuminators, when the voltage in a LED exceeds a threshold value of the release voltage, the value of the current increases without limit, which is why the current of LEDs usually has to be limited by an external component, e.g. a resistor. Since the efficiencies of new LEDs are constantly on the increase, it is no longer economical or even technically possible to connect LEDs in series and limit the current of a single LED by a resistor; instead, an electronic low-loss coupling element, a so-called chopper power supply, is to be used for the purpose.
Such a chopper power supply enables current to be supplied to a LED from a higher current to limit the current to a correct value for the LED with very small losses. An example is e.g. a current of 300 mA to be taken for a LED of 1000 mW. In such a case, a chopper drops the current about 20 V which, limited by a resistor, causes a power loss of approximately 6 W. This means an electric efficiency of only approximately 15% for the entire coupling. When the supply voltage is 230 V, the efficiency is only a fraction of the above. When the illuminating efficiency of the LED is also taken into account, the illuminating efficiency of the entire coupling is only approximately 2 to 3%. The corresponding total electric efficiency of the chopper per power supply is approximately 95%. In low-power LED solutions, this power loss has no economic importance but when one single application may comprise several dozens of LED lights, the power loss becomes important and at the same time the inside temperature of the illuminator rises, which, in turn, shortens the life of the LEDs and other components. Therefore, the prior art illuminator solutions no longer suit economically to be used in illuminators comprising a plurality of high-power LEDs of 0.1 to 5 W.